Tub apparatus

ABSTRACT

Tub apparatus includes a foamed resiliently compressible plastic tub wall having an inner side and an outer side, the tub having an interior to receive liquid; a tensile liner adjacent the wall side, the liner and characterized in that it resists outward expansion in response to loading exerted by liquid filled into the tub interior; and including ports extending through the side wall and liner for circulating liquid between the interior of the tub and the exterior thereof. The plastic wall is typically locally heat cored in situ and provided with elbow fittings having venturis for efficient water, and water and air flow.

This application is a continuation-in-part of Ser. No. 145,233, filedJan. 19, 1988, now U.S. Pat. No. 4,858,254 which is acontinuation-in-part of Ser. No. 891,232, filed July 30, 1986 now U.S.Pat. No. 4,843,659.

BACKGROUND OF THE INVENTION

This invention relates generally to hot tubs or spas, and moreparticularly to a low-cost, light-weight, insulated, semi-rigid plasticspa, which is easily portable, and hot water supply means therefor.

Conventional hot tubs are heavy, non-portable, and expensive in theirconstruction; also, excessive electrical and heat energy is required fortheir operation. There is need for a greatly improved spa structure withthe unusual advantages in construction, modes of operation, use andtransport, and results, as are now made possible by the presentinvention, as will appear.

SUMMARY OF THE INVENTION

It is a major object of the invention to provide a hot tub or spameeting the above needs. Basically, the inexpensive, light-weight tubapparatus comprises:

(a) a foamed plastic wall having an inner side and an outer side, thetub having an interior to receive liquid,

(b) a tensile liner adjacent the wall side, the liner and characterizedin that it resists outward expansion in response to loading exerted byliquid filled into the tub interior,

(c) and including ports extending through the side wall and liner forcirculating liquid between the interior of the tub and the exteriorthereof.

It is a further object to provide a non-stretchable flexible liner thatincludes a plastic foam layer bonded to the interwoven strips and alsoto the wall inner side. As will be seen, the plastic strips may consistof pre-stretched polyethylene, and the mesh formed by the interwovenstrips is typically embedded with a plastic coating to prevent leakageof liquid through the liner.

If the liner is applied to the inner side of the tub wall, a similarliner may also be applied to the outer surface of the wall defined bythe spiral wound layers, to resist wall expansion, and a plastic jacketmay be applied over the composite wall, as thus formed. Other objectsare to provide tubular fitting aeration tubes and water flow ductsinstalled into the wall via cored passages and slits extending alongside such passages, as well as heat cut ports, all in the tube wall.

The method of constructing the tub apparatus basically includes:

(a) winding the wall sheet in a spiral to form spiral convolutions andprogressively bonding together the spiral convolutions during thewinding, thereby to form an upstanding tub wall having an inner side andouter side, and a tub interior,

(b) bonding a liner to the wall inner side to resist outward expansiontoward the wall in response to loading exerted by liquid filled into thetub interior,

(c) and slitting the tub wall, and coring the wall to enable insertionof tubular fitting and plastic ducting for supply of water to anddrainage of water from the tub interior.

Bonding is typically affected by heating the side of the liner to tackystate, and pressing the heated side of the liner against the side of thetub wall. The liner also typically includes a plastic foam layer bondedto the interwoven strips, and the heating heats a surface of the plasticfoam layer to tacky state; and a roller it typically employed toprogressively press the liner toward the wall, and the liner is fedabout the roller to present the surface of the foam layer away from theroller for heating.

These and other objects and advantages of the invention, as well as thedetails of an illustrative embodiment, will be more fully understoodfrom the following specification and drawings, in which:

DRAWING DESCRIPTION

FIG. 1 is a perspective view of spa equipment embodying the invention;

FIG. 2 is an enlarged section on lines 2--2 of FIG. 1;

FIG. 3 is an enlarged section showing construction of the spa side walland bottom wall;

FIG. 4 is an enlarged section showing interior construction of the spaunit cover;

FIG. 5 is a wiring diagram;

FIGS. 6 and 6a are enlarged views showing tub wall structure;

FIGS. 7a and 7b show plastic strips;

FIG. 8 shows a mesh formed by interwoven strips, and coated withplastic;

FIG. 9 shows a completed liner;

FIG. 10 shows bonding of a liner to the tub wall;

FIG. 11 shows a completed tub with lining or linings applied; and

FIG. 11a is a fragmentary view showing a jacket applied;

FIG. 12 is a plan view of a spa tub showing port location;

FIG. 12a is a plan view of a spa tub showing port location;

FIG. 13 is a perspective view of a portion of a tub, showing slitforming between port location;

FIG. 14 is a vertical section showing coring of the FIG. 13 tub portion,via the formed slit;

FIG. 14a is an end view of a coring tool;

FIG. 15 is a vertical section showing the location of a vertical airpassage formed in the tub wall to intersect a cored passage, and formingof the convex top rim of the wall;

FIG. 16 is a perspective view of a tubular elbow, with attached verticalpipe, and horizontal ducting, to be inserted into the cored passage, viathe formed slit;

FIG. 16a is a horizontal section showing the FIG. 16 elbow in installed(inserted) position in the tub wall;

FIG. 17 is a plan view of a T-shaped tubular fitting installed in thewall, for spa drain purposes;

FIG. 18 is a vertical section through a tub wall showing cushioning fortop closure sealing; and

FIG. 19 is a vertical section showing an alternative connections of apump, to the spa ports;

FIG. 19a is an enlarged section showing use of protective plastic; and

FIGS. 20-22 are sections through the wall fittings.

DETAILED DESCRIPTION

In FIGS. 1-3, the apparatus 10 includes a tub 11 having an insulative,annular side wall 12, and a bottom wall 13 attached to side wall. Theside wall comprises a foamed plastic sheet or sheets 14 wound in aspiral about the tub axis 15, to form multiple layers. As is clear fromFIGS. 2 and 3 the sheet is maintained to have width approximating theheight of the side wall 12, during such winding, the layer havingapproximately the same width (height in FIGS. 2 and 3). The latter arebetter indicated at 16 in FIG. 6, with glass fiber reinforcement screenmaterial 17 optimally fitted between the foamed plastic layers 16. Suchlayers may typically consist of polyethylene foam of between 1/8 and 3/8inch thickness, as for example, about 1/4 inch thickness; and, if used,the glass fiber screen may define about 1/2 inch square open spacesbetween woof strands and between warp strands. The polyethylene layersare rapidly joined together as by engagement of the outermost layer,during spiral winding, with a heating flame 18 and a roller 19, as seenin FIG. 6a. The pressure roller presses the heated inner surface of theoutermost layer 17' against the flame heated outer surface of the nextinner layer 17" to establish fusion contact, as for example through thespaces between warp strands 20, and also between woof strands extendingat 90° to strands 20. Thus, an integral relatively stiff and very sturdyspiral fusion laminated light-weight side wall 12 is gradually formedduring the spiral winding process; and a person may sit comfortably onthe top edge or rim 12a of the wall 12 without damaging it or the tubconstruction.

The tub bottom wall 13 has a similar construction except that parallelsheets 13a (5/8 inch thick) of cross linked polyethylene foam, with orwithout glass fiber layers 12 therebetween, are heated fusion welded toform an integral bottom wall. The latter is then peripherally fusionwelded as at 22 to the bottom of the side wall. A plastic jacket 23 maybe fitted about both the side wall and bottom wall. Jacket 23 sheets mayconsist of foamed, reinforced, marine vinyl resin; and include innersheet 23a, outer sheet 23b, crest sheet 23c, and bottom sheet 23d, alljoined together to form an internal waterproof decorative jacket, asshown. Jacket lower edge extend may be looped as at 23e, and a drawstring fitted in the loop to be drawn tight and attach the jacket to thewall 12. A welded seam is indicated at 23f. The vinyl jacket may haveselected weatherable color.

A tub cover is shown at 25 in FIG. 4, with generally the same spiralpolyethylene layer construction, as does wall 12. Thus, spiralpolyethylene layer or layers 26 extending about vertical axis 27 can befusion welded together, similar to the wall section but typicallywithout the fibers. Additional structural stiffness may be imparted tothe cover by creating thermally densified layers on each face, 26 and28. These are created by compressing the spiral wound structure betweentwo hot plattens. A vinyl jacket 29 is fitted about the polyethylenewindings, and is held in place by a draw string in loop 29a.

FIG. 2 shows upper and lower ports formed through the tub wall as bytubular plastic fittings 30 and 31. Water circulating means 32 isconnected with those ports, and includes a pump 33 for circulating waterinto the tub interior 34 via upper port 30a, and for withdrawing waterfrom the tub interior 34 as via lower port 31a. A filter 35 is locatedwithin the tub to filter the water being withdrawn through port 31a, sothat dirt and small objects are not fed to the pump lower inlet 33a. Thefilter is easily withdrawn upwardly at the tub interior, for cleaning orreplacement. The pump discharges sidewardly at outlet 33b, and plasticpiping extends upwardly at 36 to deliver pressurized and heated water toport 30a, and an associated venturi.

The water circulating mean includes an electric motor connected indriving relation with the pump, and includes a shunt duct connected withthe water circulating mean and located to receive heat generated byoperation of the motor to heat a side stream of the water passingthrough the shunt duct. The illustrated shunt duct includes metallictube 40 wound about the pump drive motor 45 to receive heat from same,for heating the tub water, whereby extreme simplicity and energy savingsare realized. The duct 40 has an end connected at 40a into the watercirculating system proximate pump outlet, i.e. into piping upper branch36; its opposite end connected as at 40b into the water circulationsystem proximate pump inlet 33a, i.e. in lower piping branch 43extending from port 31a to inlet 33a. Accordingly, water flows in theshunt duct from a higher (pressurized) level to a lower level; and aportion of the water flowing through the pump is heated and re-heated,for highly efficient heating action. Thus, no external source of heatfor the hot-tub water is required, and motor 45 serves multiplefunctions, its waste heat being efficiently utilized. The height of theinlet and outlet of the shunt duct are approximately the same tominimize thermosyphon action when the motor is off. The thermosyphonaction can cause a momentary surge of extra hot water to trip the highlimit switch 49.

In the schematic of FIG. 5, the motor coil 45a is supplied withelectrical energy from a plug 46, such as is insertible into a household120 volt outlet coil includes line 47 with which thermostat switch 48,and high limit switch 49 are connected in series. Switch 48 is operatedby a thermostat sensor 49 applied to inlet port 30a, whereby if thewater is too hot, the motor is shut down. Limit switch 49 is alsocontrolled by temperature sensor 50 located adjacent the tub to shut themotor down if the tub becomes overheated. Line 47 and return line 47apass through cord 52, and through a ground fault interruptor 53, asshown.

A plastic shell enclosure or housing for the pump and motor is indicatedat 60. It is well insulated to keep the heat generated by the motorinside where it can be transmitted to the water, and to minimize soundfrom the motor and pump inside for the comfort of the users. It is acompact package which facilitates ease of transport and set-up of same.

In FIG. 11 the tub apparatus 111 includes an insulative, bottom wall 113supporting the side wall, as by attachment to the lowermost extentthereof, at 113a. The side wall comprises a foamed plastic sheet orsheets 114 wound in a spiral about tub axis 115, to form multiplelayers. Such layers may typically consist of polyethylene foam ofbetween 1/8 and 3/8 inch thickness, as for example about 1/4 inchthickness. The layers are rapidly joined together as by engagement ofthe outermost layer, during spiral winding, with a heating flame, asdescribed above in connection with FIG. 6a; however, no glass fiberscreen is employed.

Instead, an inner liner 117 is provided adjacent the wall inner side112a. As indicated in FIG. 9, that liner comprises interwoven strips118a and 119a of pre-stretchable plastic material characterized in thatthe liner resists outward expansion toward wall 112 in response toloading exerted by liquid such as water 121 in the tub interior See FIG.11. Therefore, the tub wall 112 is not deflected or stretched radiallyoutward, as it would be in the absence of the liner.

FIG. 7a shows a typical thermoplastic (such as polyethylene) strip 118or 119 prior to pre-stretching, endwise, in the direction of arrows 123and 124. FIG. 7b shows the same strip 118a or 119a after suchstretching, with a correspondingly reduced width, to provide hightensile strength. FIG. 8 shows the strips 118a and 119a closelyinterwoven with warp 118a and woof 119a strand or strip layer or meshpattern 125. The woven strips are then embedded in or coated with aplastic coating 125a to prevent leakage of liquid therethrough and toprovide load spreading. The plastic coating may also consist ofpolyethylene. Such a mesh is a product of Chave and Early, New York, NewYork, and sold under the name "CE-TEX".

FIG. 9 shows the completed liner 117, which includes a plastic foamlayer 126 bonded in face-to-face relation with one side of the coatinglayer 125a. The layer 126 may for example consist of polyethylene foam.The bond interface is indicated at 128, and may be formed by heatfusion.

As a result, the composite liner 117 may be fusion bonded to the innerside 112a of the spiral layer wall 112. FIG. 10 shows that process.Bonding is carried out by heating the outer side 126a of the layerand/or the side 112a, to tacky state, and then pressing the hot tackyside 126a against the side 112a of spiral layer wall 112. Liner 117extends more than 360° around the tub, to provide overlap. Heating iseffected by directing flame 130 or other heat source heat against sides126a and/or side 112a, as seen in FIG. 10, and as the liner isprogressively fed in direction 131, a pressure roller 132 rollingagainst the applied liner to press side 126a against side 112a.

FIG. 11 also shows a like liner 117' applied against the outer side112a' of the wall 112, to also resist outward stretching of the wall 112and also to add toughness. Finally, a jacket 133 like jacket 123 may beapplied or attached to the inner surface 135 of the completed tub walland to tub bottom wall 113, or to the liner 117. See FIG. 11a, thejacket applied in the same manner as in FIG. 3. A tub wall upper rimappears at 137, in FIG. 11. Jackets 123 and 133 may have the sameconstruction as tensile liner 117.

In the above FIGS. 10, 11 and 11a, the lined tub wall indicated bylayers 114 may instead be a single layer of foam.

From the foregoing it will be understood that the primary purpose of thetensile band or liner 117 is to absorb the hoop stress caused by thepressure resulting from the column of water in the tub. Without suchtensile band, the water pressure places continuous compression andtensile stresses o the inner side of the tub wall. The polyethylene foamwalls or layers 114 expand, especially at the bottom, in the absence oftensile band 117. That band also provides improved wall toughness andreduced communication of fluids between tub walls and outsideenvironment.

A like tensile band in the wall between the inner and outer sides of thewall may be employed to absorb hoop stress while allowing somecompression and compliance of foam inside tensile band. One such layer,as seen in FIG. 11, may be considered to represent such an intermediateband.

An O.D. tensile band as at 117' is usable to absorb loads from peoplesitting on the tub wall, improve O.D. toughness, improve aesthetics, andreduce communication of fluids between tub walls and environment.

Liner materials or composites may be constructed to have enough tensilestrength to act as tensile band. Typically materials include vinyl filmor films laminated to polyester fabrics and polyester fabrics coatedwith vinyls. Unattached and/or attached tensile band materials includemetal foil, glass fibre reinforced polymers, aluminum sheet, coated anduncoated polyester fabrics films laminated to polyester fabrics, spunbonded polyester fibres, tensilized polyester films, and tensilizedpolyethylene films slit to thin strips and woven in two axes and coatedwith polyethylene as described herein. Thin layers of PE/EVA, PE, EVA,XLPE, and/or PVC foam may be attached to the inside of the tensile bandto reduce water transport, improve aesthetics and/or feel, from insidethe tub, to act as a tie layer, and to act as a compression element forplumbing seals.

Fibre or filament molecular orientation is preferably generallycircumferential; however, biaxial and random orientation are alsopossible.

Tensile band or bands may be attached to a liner for a tub wall innersurface, as via adhesive, solvents, and/or thermal fusion techniquesincluding radio frequency heat sealing and ultrasonic welding. Tielayers may be used to make material attachment easier, via improvedbonding compatability, to add stiffness, to reduce leakage, and/orimprove aesthetics and feel.

Intermediate tensile bands (between I.D and O.D.) may use theabove-described materials, or glass fibers and polymer fibers in loose,uni-directional and bi-directional fabrics, fused between layers ofpolyethylene foam during wall construction. Outer side tensile bands maybe fastened using above methods, or by shrinking on the tub outer wall.

Tensile band material candidates are typically available as rolls andmust be overlapped to create a circumferential tensile band. Althoughtensile bands spirally wound into the tub wall may be overlapped withoutdirect connection, I.D. and O.D. tensile bands typically require joiningas via solvents, adhesives, mechanical fasteners and/or thermal fusiontechniques.

A tensile band acting as liner, or attached to a liner, may be providedto add stiffness to the liner and thereby ease fitting to the inside ofthe tub. Additionally, this configuration toughens the liner and may beused along with a foam layer as a mechanical plumbing seal.

Referring now the modified tub of FIG. 12, it shows the locations ofports in the tub wall 299 as during construction of the tub, followingforming of the spiral layer wall, as described above. Inlet and outletports are shown at 300 and 301, with T-shaped tubular fittings 302 and303 in those ports. The ports extend only part way into the tub wall,from the outer side thereof, and are formed as by use of electricallyheated circular wire or knife 305 applied to the wall, in a radialdirection. The drain port 301 is below and lower than the inlet port300, as shown in FIG. 12a.

Also shown are the location of two jet inlet ports 306 and 307 formedradially outwardly from the inner side 299a of the tub wall, and at 180°spacing about the tub axis 308. Two outlet ports 309 and 310 are alsoformed radially outwardly from the inner side 299a of the tub wall, andat about 90° spacings about axis 308.

Next, slits are cut into the tub wall, including slits 311 and 312respectively between inlet 300 and the jet ports 306 and 307, and slits313 and 314 respectively between the drain port 301 and the outlet ports309 and 310. Slits 311 and 312 may be cut into and from the inner sideof wall 299a, at the level of port 300 and slits 313 and 314 may be cutinto and from the outer side of the wall, at the level of port 301. Theslits are cut to depths allowing insertion of a coring tool 315 (seeFIG. 14a) into port 300 for example, and then travel of the toolcircumferentially into alignment with first port 306, and the port 302.The tool 315 has an electrically heated circular metal band 316, thatcores the passages 311a and 312a associated with slits 311 and 312, withelectrical leads 317 and 318 that mount band 316 and pass radiallythrough and along the slit (311 or 312) as the tool is movedcircumferentially. Heating of the band is to temperatures that melt thethermoplastic of the wall, in situ, as the band is advanced, after thewall is coil-formed. The severed tubular core pieces are then pulled outthrough the slits. In similar manner, passages 313a and 314a associatedwith slits 313 and 314 are formed by tool 315. Note that the formedpassages extend through adjacent layers of the wound plastic wall.

Next, aeration passages 320 are formed vertically above the injectionports 306 and 307, as seen in FIG. 15. Also, the top rim of the wall isshaped to be convex upwardly. FIG. 15 shows an electrically heated,curved cutter band 321 being advanced lengthwise (normal to the plane ofFIG. 15) around the tub rim to sever material above the band. Noteelectrical leads 322 and 323.

Next, water injection elbow tube duct assemblies, as seen in FIG. 16,are inserted (by pushing them) into ports 306 and 307, so that theplastic elbows 324 are received in the ports, air inlet plastic tubes325 are received in the passages 320, and flexible plastic ducts 326 arereceived in the cored passages 311a and 312a (by pushing them radiallythrough the slits 311 and 312) and extending toward port 300. FIG. 16ashows the injection elbow interior construction, with a venturi 328receiving water from duct 326 and jetting aerated water from the elbowinto the tub interior. The venturi receives air from the aeration tube325 and air flow regulatory means appears at 325d. See jet 328a. Passage320 and tube 325 extend to upper rim 299c of the tub wall. As seen inFIG. 22, a wall fitting 380 has fit at 381 with box end 324a of theelbow 324, and a flange 382 on the wall fitting clamps an annular seal383 against the tub jacket 360 to establish a seal. Plenum 328a receiveswater from the venturi 328, mixed with air supplied by duct 325 toannulus 325a to exit at 325b and mix with the water flow.

FIG. 17 is a section showing a tee 329 having a stem 329a as fitted intoeach of the entrance and drain ports 300 and 301. The tubular tee head329b is in alignment with passages 311 and 312 and connected with ducts311a and 312a therein; and a similar tee head 329b is in alignment withpassages 313 and 314 and connected with ducts 313a and 314a therein.Tubular connection fittings 330 and 331 are connected with stem 329a,and are connectible with external ducting (see duct 331 in FIG. 19).Elbow 370, as seen in FIG. 21, may be inserted at ports 309 and 310.Water flows from the tub into inlets 371 and through a venturi 372. Itthen turns at 373 and flows to a plastic tube 374 in core 313 or 314.Smooth flow in 374 is then established.

FIG. 19 shows the by-pass duct 333 that has metallic heat conductivewindings 333c about the motor 336 to receive heat therefrom, has itsintake at 333a at elbow 323, and its exit or discharge end at 333b, thethroat of venturi 334 in duct 331. Therefore, heat from the motor istransferred to the water passing directly to the tub interior via jetsat 306 and 307, and the pressure differential between 333a and 333bfacilitates flow in the by-pass duct 333. Water draining from the poolat port 301 passes via duct 332 to the intake 340 of centrifugal pump341 driven by the motor. The pump discharge, at 342, passes via metallicriser duct 343, plastic elbow 344, venturi 334 and plastic duct 331 totub intake port 330. Temperature control sensors 350 are applied to themetallic riser duct 343 to sense the temperature of the water flowing tothe spa, and those sensors are covered by a plastic foam sheath 354. Acontrol 355 receives input from the sensors, and controls a valve 356 inthe by-pass duct, increasing the closing of that valve if the watertemperature rises above a pre-set limit, and vice versa. A filter 361 inthe spa tub removes particulates from the water recirculated to the tubinterior via duct 331.

FIG. 19a shows the use of heat conductive thermal mastic at 450 betweenthe motor and the windings t conduct heat efficiently from the motor tothe coil. An example is the product T-70, produced by ThermalIndustries, Texas.

In FIG. 18, a vinyl jacket 360 fits over the tub wall 299, and over thetensile liner 361 adherent to the inner side of the wall, to seal offthe slits 311,312, 313, and 314 referred to. An annular resilientcushion 362 inside the jacket, near the top of the wall provides aninterference fit with a tub cover 365, as shown, sealing off the tubinterior. The cushion may consist of open cell urethane foam. The elbowand drain fittings have sealing engagement with the jacket, as viaclamping flanges 366, seen in FIG. 17. The jacket 360 forms openings inalignment with the ports, as at 306, 307, 309, and 310.

The fitting seen in FIG. 20 may be employed at the connection betweenduct 330 and duct 331. These ducts have ends 330a and 331a urgedtogether as annular coupling 390 bridging such ends is rotatablytightened. Coupling 390 has internal threads 391 engaging externalthreads 392 on duct 331; and it has an internal shoulder at 393 engagingexternal shoulder 394 on duct 330.

We claim:
 1. The method of forming a relatively lightweight plastic tubside wall that passes tub liquid, and employing an elongated sheetformed of foamed thermoplastic material that includes the steps:(a)progressively winding said sheet in a spiral fashion about an axispassing through the center of the space to be enclosed by said sidewall, (b) heat fusing together successive foamed plastic sheet layers toform a unitary group of convolutions, (c) providing openings to extendin said wall for passing tub liquid, by locally cutting away saidmaterial across multiple of said convolutions, said cutting away stepincluding forming a slit or slits in said wall, (d) said cutting awaystep being carried out to form a tunnel or tunnels in said wall,inwardly of said slit or slits.
 2. The method of claim 1 wherein saidcutting away step is carried out by heat cutting of the plastic wallmaterial.
 3. The method of claim 1 including inserting a duct or ductsinto said tunnel or tunnels, to pass said liquid.
 4. The method of claim1 including providing a stretch resistant liner and locating the lineradjacent the side of said wall to resist outward expansion in responseto loading exerted by liquid filled into the tub interior, as viaopenings locally cut in said wall.
 5. The method of claim 1 includingforming both liquid passing and gas passing passages in said wallconvolutions.
 6. The method of claim 1 wherein said heat fusing iscarried out by heating the surface of the sheet approaching a locus ofwinding juncture of the sheet with a wound convolution, said heatingbeing such that said heated sheet surface bonds to said woundconvolution.
 7. The method of claim 1 including rotatably driving saidunitary group of convolutions about said axis during said heat fusing.8. The method of claim 4 including cutting said openings to form portsthat extend through said side wall and through the liner for passingliquid between the tub interior and exterior.
 9. The method of claim 8that includes providing said liner to comprise two layers of plasticmaterial that have been bonded together, one layer consisting of foamedplastic.
 10. The method of claim 4 including providing a flexiblejacket, and closely fitting the jacket to said wall, and forming tubliquid passing openings through said jacket and in said wall.
 11. Themethod of claim 6 including employing a roller to effect localpressurization at said winding juncture of the sheet approaching thatlocus and the wound convolution.
 12. The method of claim 7 includingexerting endwise tension on the sheet material being wound on saidunitary group of convolutions.
 13. The method of forming a relativelylightweight plastic tub side wall that passes tub liquid, and employingan elongated sheet formed of foamed thermoplastic material that includesthe steps:(a) progressively winding said sheet in a spiral fashion aboutan axis passing through the center of the space to be enclosed by saidside wall, (b) heat fusing together successive foamed plastic sheetlayers to form a unitary group of convolutions, (c) forming both liquidpassing and gas passing passages in said wall convolutions, (d) a liquidpassing passage being formed to have elbow configuration, and a gaspassing passage being formed to intersect said elbow configuration. 14.The method of claim 13 including inserting a hard plastic tubular elbowinto said elbow-shaped passage, and jetting tub liquid into the tubinterior via said hard plastic elbow, and aspirating gas into the jettedliquid via the gas passing passage.
 15. The method of claim 14 includinginserting a hard plastic duct into said gas passing passage tocommunicate with the interior of said hard plastic elbow, and passinggas to said hard plastic elbow via said hard plastic duct.
 16. Themethod of claim 15 including extending said gas passing passage toterminate at or proximate an upper rim defined by said wall.
 17. Themethod of forming a relatively lightweight plastic tub side wall thatpasses tub liquid, and employing an elongated sheet formed of foamedthermoplastic material that includes the steps:(a) progressively windingsaid sheet in a spiral fashion about an axis passing through the centerof the space to be enclosed by said side wall, (b) heat fusing togethersuccessive foamed plastic sheet layers to form a unitary group ofconvolutions. (c) said material being resiliently compressible, as issaid wall, and maintaining said sheet to have width approximating theheight of said wall, during said winding, (d) and attaching an innerunitary liner adjacent the side wall during said winding step, the linercharacterized as formed of pre-stretched plastic material that resistsoutward expansion toward said wall in response to loading exerted bywater in the tub interior.
 18. The method of claim 17 includingproviding a flexible jacket, and closely fitting the jacket to saidliner, and forming tub liquid passing openings through said jacket, saidliner, and in said wall.
 19. The method of claim 17 including heatcutting plastic material proximate an upper rim defined by said wall,thereby to form an arcuate upper rim, crosswise of multiple of saidconvolutions.
 20. The method of forming a relatively lightweight plastictub side wall that passes tub liquid, and employing an elongated sheetformed of foamed thermoplastic material that includes the steps:(a)progressively winding said sheet in a spiral fashion about an axispassing through the center of the space to be enclosed by said sidewall, (b) heat fusing together successive foamed plastic sheet layers toform a unitary group of convolutions, (c) providing a stretch resistantliner and locating the liner adjacent the side of said wall to resistoutward expansion in response to loading exerted by liquid filled intothe tub interior, as via openings locally cut in said wall, (d) cuttingsaid openings to form ports that extend through said side wall andthrough the liner for passing liquid between the tub interior andexterior, (d) and including providing a pump and assembling the pump tothe tub to pump tub liquid into the tub interior, via at least one ofsaid ports, and providing means for transferring heat from the motor totub liquid being pumped.
 21. The method of claim 20 includingtransferring motor heat to a by-pass stream of tub liquid circulatingabout the motor, and aspirating said by-pass stream into the liquidbeing pumped to the tub interior.
 22. The method of forming a relativelylightweight plastic tub side wall that passes tub liquid, and employingan elongated sheet formed of foamed thermoplastic material that includesthe steps:(a) progressively winding said sheet in a spiral fashion aboutan axis passing through the center of the space to be enclosed by saidside wall, (b) heat fusing together successive foamed plastic sheetlayers to form a unitary group of convolutions, (c) said material beingresiliently compressible, as is said wall, (d) providing a flexiblejacket, and closely fitting the jacket to said wall, and forming tubliquid passing openings through said jacket and in said wall, (e) andproviding a resiliently compressible cushion against the jacket, and atthe inner side of the wall, and fitting a tub cover into the uppermostinterior of the tub, to compressively interfere with said cushion.